The present invention relates to a wavelength division multiplexer (WDM) and, more particularly, to an optical WDM that is a reflective system and is integrated.
Optical WDMs enable light of multiple wavelengths to be spatially dispersed such that each wavelength of light is spatially separated from every other wavelength of light. WDM devices typically comprise two major functional portions. The first portion provides spatial demultiplexing (i.e., the dispersion) of the individual wavelengths through the use of a grating (e.g., an array waveguide grating, a filter array, etc.). The second portion then acts on one or more of the spatially dispersed wavelengths for purposes of, for example, attenuation, monitoring, compensation or switching.
In a reflective system, these wavelengths are then sent back through the same dispersion element, thereby multiplexing them (i.e., combining the wavelengths) again onto one optical fiber. In fiber optic networks, reflective WDM systems are increasingly being used because of their lower complexity, smaller size and lower part count compared to transmissive WDM systems. However, the use of a reflective system requires the use of circulators to separate the incoming and outgoing signals. Circulators are often expensive and difficult to integrate into a small optical system. In addition, systems using polarization sensitive elements are more complex and require another circulator-like separation stage to route a signal between the different ports. In addition to having a large part count, these types of systems typically require precision alignment of several optical components, which is time consuming and expensive.
Accordingly, a need exists for an optical WDM device that is a reflective system., but that is smaller in size than known reflective WDM systems, that has a smaller part count than known reflective WDM systems, that does not require a circulator, and that does not require alignment of optical components.
The present invention provides an integrated, reflective optical WDM device comprising optical components that are integrated together to provide a reflective WDM device that does not require any circulators, that has simplified alignment due to its integrated characteristics, and that is relatively low in cost. The WDM device comprises the integrated port separator, a dispersive element and a reflector.
The integrated port separator comprises various optical components that spatially separate the polarization components of a light beam input through an input port of the integrated port separator. The spatially separated polarization components are output from the integrated port separator and impinge on the dispersive element, which spatially separates the wavelengths associated with the polarization components impinging thereon. The spatially separated wavelengths then impinge on the reflective element and are reflected with angles of polarization that depend on the state of the reflective element. The reflected polarization components maintain their respective wavelengths when they are reflected. However, when they are reflected, they are directed along a path through the integrated port separator that depends on the angles of polarization of the reflected polarization components, which depends on the state of the reflective element.
Preferably, the reflective element comprises an array of liquid crystal display (LCD) pixels, each of which is individually controllable. Thus, the path of each polarization component through the integrated port separator depends on the state of the LCD pixel upon which the polarization component impinges, which depends on the wavelength associated with each polarization component and the manner in which the dispersive element spatially separates the wavelengths to cause the corresponding polarization component to impinge on the reflective element.